On Thu, 11 Aug 2022 12:13:29 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote: > When page migration happens, we always ignore the young/dirty bit settings > in the old pgtable, and marking the page as old in the new page table using > either pte_mkold() or pmd_mkold(), and keeping the pte clean. > > That's fine from functional-wise, but that's not friendly to page reclaim > because the moving page can be actively accessed within the procedure. Not > to mention hardware setting the young bit can bring quite some overhead on > some systems, e.g. x86_64 needs a few hundreds nanoseconds to set the bit. > The same slowdown problem to dirty bits when the memory is first written > after page migration happened. > > Actually we can easily remember the A/D bit configuration and recover the > information after the page is migrated. To achieve it, define a new set of > bits in the migration swap offset field to cache the A/D bits for old pte. > Then when removing/recovering the migration entry, we can recover the A/D > bits even if the page changed. > > One thing to mention is that here we used max_swapfile_size() to detect how > many swp offset bits we have, and we'll only enable this feature if we know > the swp offset is big enough to store both the PFN value and the A/D bits. > Otherwise the A/D bits are dropped like before. > There was some discussion over v3 of this patch, but none over v4. Can people please review this patch series so we can get moving with it? Thanks.
